Linux has no "binary backwards compatibility" or "legacy poor-security garbage design" to stick to. At least, not nearly to the extent Microsoft products do. And it has no real, market-driven (commercial) reason to.

Malware that is injected into warez is not taking advantage of backwards compatibility. It has nothing to do with "legacy poor-security garbage design" either. There is no isolation layer within Linux that would protect it from a trojan injected into an executable.